1. Field of the Disclosed Subject Matter
The disclosed subject matter is in the field of the ophthalmology, more particularly, diagnostic retinal imaging, for example, of retinal circulation, and concerns systems and methods for constructing a widefield image of the retina from a plurality of retinal images, comprising a base image and a plurality of peripheral images. The techniques disclosed herein enable medical observations of retinal phenomena in patients, such as retinal vein occlusion, artery occlusion, retinal detachments, intraocular inflammation, ocular tumors, and the like, which were difficult to detect and impossible to quantify under prior art approaches.
2. Description of Related Art
Imaging of the retinal circulation has principally been done with fluorescein angiography in which the image is typically recorded with a fundus camera or a scanning laser ophthalmoscope. With a fundus camera the peripheral portion of an objective lens is used to focus light to illuminate the fundus and the central portion of the objective lens is used to create a real, inverted image of the fundus within the body of the camera. Additional optical elements are used to project the real image onto the imaging plane. The scanning laser ophthalmoscope uses a rotating mirror system to steer laser illumination across the fundus and an objective lens is used to gather the reflected light. The field of view of commercial fundus cameras ranges from 30 to 60 degrees and from commercial scanning laser ophthalmoscopic systems from 10 to 30 degrees. Shifting the axis of either of these devices allows observation of more peripheral portions of the patient's eye, but with decreasing image quality secondary to decreasing width of the entrance pupil, vignetting, and induced astigmatism.
One approach that has been used to overcome limitations inherent in conventional lens based systems with coaxial illumination, is the use of a widefield imaging system based on an ellipsoidal mirror. See Anderson, D C, Lucas, R A, Henderson, R. U.S. Pat. No. 5,815,242 (“Wide Field Scanning Laser Opthalmoscope [sic]”), incorporated herein by reference. The approach of Anderson, et al. is illustrated in FIG. 1 hereto. Elliptical mirrors have two conjugate focus points (FIG. 1A); extending this idea to three dimensions by rotating the ellipse would create an ellipsoidal surface capable of focusing light rays emanating from the eye (FIG. 1B). The retina is illuminated by a laser, the spot of which is scanned over the ellipsoidal surface to illuminate the conjugate point in the fundus. Using this technique, the Optos P200 Scanning Laser Ophthalmoscope (Optos North America, Marlborough, Mass.) has a stated field of view of 200 degrees.